Publications

The standard method for CHAMP (CHAllenging Minisatellite Payload) GPS occultation data processing at GeoForschungsZentrum (GFZ) Potsdam is a double difference technique. GPS satellite and ground station data are combined to correct for clock parameters of CHAMP and the occulting and referencing GPS satellites, respectively. The application of the double difference method requires a continuous data stream from a global network of GPS ground receivers. Termination of the Selective Availability (SA) mode of the GPS on May 2, 2000 at 04:05 UTC reduced the drift rates of the GPS clocks by orders of magnitude. This made the clocks more predictable and enabled the application of single differencing techniques for occultation data processing to become a potentially attractive alternative. The short-term variability of the GPS clocks before and after termination of SA and consequences for the accuracy of vertical temperature profiles are discussed. By using 5-min GPS clock solutions, a space-based single difference technique without direct use of GPS ground station data is applied to a set of 436 CHAMP occultations, measured during April 19-21, 2001. The 5-min GPS clock solutions are automatically computed as part of the GPS Precise Orbit Determination for CHAMP by use of 1/30 Hz data of the GPS ground network for CHAMP. The comparison to a reference data set, generated using the double difference method yields no discernible temperature bias below 30 km altitude, a standard deviation of <0.6 K below 20 km and <1.2 K below 30 km. Statistical comparisons of both data sets shows mean differences and standard deviations from meteorological analyses that are nearly identical to within 0.15 K up to 30 km.

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Wickert, J.; Beyerle, G.; Hajj, G. A.; Kirchengast, G.; König, R.; Schmidt, T.; Marquardt, C.; Reigber, C. (2002): Space-based single differencing: An alternative approach for CHAMP GPS occultation data processing. 27th General Assembly European Geophysical Society (EGS) (Nice France 2002).